Projectors are devices that use a display element such as a liquid crystal device (LCD, LCOS), a DMD or the like as a light valve, so that the display image thereof is enlarged and projected onto a screen or the like by means of a projector optical system. As a result of ever more demanding performances (high-pixel counts) in display elements, there have been proposed various high-performance projectors that afford both high resolution and sufficient correction of various aberrations (for instance, Japanese Unexamined Patent Application Laid-open No. 2004-279958).
In high-performance projector optical systems, however, the lens count increases for the sake of achromatism, which results in greater system size and precludes achieving a smaller size of the projector as a whole, all of which is problematic.